CN113363482B - Composite binder for silicon-based negative electrode of lithium ion battery and preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of lithium ion batteries, and discloses a composite binder for a silicon-based negative electrode of a lithium ion battery, a preparation method and application thereof, wherein the composite binder is abbreviated as C-SP-CA and is prepared by uniformly dispersing sericin powder in deionized water, adding citric acid to form a mixed solution, and carrying out in-situ crosslinking reaction at 120-160 ℃. Sericin in the adhesive is composed of a large amount of amino acids such as serine and aspartic acid with hydrophilic groups on side chains, and has better dispersibility compared with the traditional PVDF adhesive. In addition, the formed three-dimensional network structure is beneficial to the transmission of electrons and ions, and the mechanical property of the binder is greatly improved, so that the electrode keeps good integrity in the circulating process. The binder prepared by the method can obviously improve the electrochemical performance of the silicon-based cathode of the lithium ion battery, and in addition, the binder has the advantages of simple preparation process, low cost and the like, and easily meets the requirement of industrialization.

Description

A composite binder for silicon-based negative electrodes of lithium-ion batteries and its preparation method and application

technical field

The invention belongs to the technical field of lithium batteries, and more specifically relates to a composite binder for a silicon-based (SiO _x ) negative electrode of a lithium ion battery, a preparation method and application thereof.

Background technique

With the continuous popularization of new energy electric vehicles, lithium-ion batteries with high energy density have become the future development direction of power batteries. At present, the anode material of commercialized lithium-ion batteries is mainly graphite, but its low theoretical capacity (372mAhg ^-1 ) is difficult to meet the demand of high energy density. Elemental silicon has a relatively high capacity (4200mAh g ^-1 ), but a huge volume expansion of up to 300% will occur during the process of extracting/intercalating lithium ions, causing silicon particles to break and pulverize, seriously affecting the cycle life of the electrode. Compared with elemental silicon, silicon oxide (SiO _x , 0<x<2) has considerable theoretical capacity (1500mAh g ^-1 ) and smaller volume change (100-150%), and is the most promising for commercial applications High-performance anode materials. However, due to the non-negligible volume expansion (about 200%), SiO _x anode materials also face fatal defects such as rapid capacity fading and poor stability.

Binder is one of the important components of lithium-ion batteries. It can bind active material particles and conductive agent particles to the current collector, maintain the integrity of the electrode structure during charge and discharge, and improve the cycle stability of lithium-ion batteries. have an important impact. Therefore, synthesizing a multifunctional composite binder is the most economical and effective method to improve the electrochemical performance of SiO _x and achieve high energy density for lithium batteries.

Polyvinylidene fluoride (PVDF) is currently the most widely used commercial binder with good electrochemical stability. However, in the face of high energy density SiO _x anode materials, PVDF and SiO _x particles form a weak van der Waals force, which is difficult to withstand the stress generated by the volume expansion of SiO _x particles during cycling, and easily causes the destruction of the electrode structure.

As a natural high-molecular protein, sericin has good water solubility and dispersibility, and is a promising binder for SiO _x anodes. However, single sericin has a linear chain structure and poor bonding performance, making it difficult to maintain the volume expansion of SiO _x particles during cycling. Based on this, the present invention proposes to design a composite binder with a three-dimensional network structure through the in-situ crosslinking reaction of sericin and small molecule citric acid, improve the mechanical strength of the binder, and realize the cycle stability of the SiO _x negative electrode .

Contents of the invention

In order to solve the problem that the binders in the prior art are difficult to solve the cycle stability of high energy density SiO _x negative electrodes, the purpose of the present invention is to provide a composite binder for silicon-based (SiO _x ) negative electrodes of lithium-ion batteries. The binder has abundant binding sites on the surface of SiO _x particles, and a strong covalent bond is formed through the cross-linking reaction, which greatly enhances the mechanical strength of the binder and can effectively inhibit the SiO _x electrode The problem of volume expansion during the cycle makes the SiO _x electrode have a stable cycle performance.

Another object of the present invention is to provide a method for preparing the above-mentioned composite binder for the _SiOx negative electrode of lithium-ion batteries, the method uses in-situ cross-linking to form a composite binder with a three-dimensional network structure.

Another object of the present invention is to provide the application of the composite binder for the _SiOx negative electrode of the lithium ion battery.

The purpose of the present invention is achieved through the following technical solutions:

A composite binder for silicon-based (SiO _x ) negative electrodes of lithium-ion batteries, the composite binder is uniformly dispersing sericin powder in deionized water, then adding citric acid to form a mixed solution, at 120 ~ Prepared by in-situ cross-linking reaction at 160°C.

Preferably, the mass ratio of the sericin powder to citric acid is (1-2):1.

Preferably, the volume ratio of the mass of the sericin powder to the deionized water is (20-30) mg:1 mL.

The method for preparing lithium-ion battery _SiOx negative electrode by described composite binder comprises the steps:

S1. adding sericin powder and citric acid into deionized water, stirring until completely dissolved, to obtain a mixed solution;

S2. Add electrode active material SiO _x and conductive agent to the mixed solution and mix and stir to obtain a uniformly dispersed electrode slurry;

S3. Apply the obtained electrode slurry to the current collector, and heat at 120-150°C. The heating process promotes the cross-linking reaction between the sericin powder and citric acid to prepare the silicon-based negative electrode of the lithium-ion battery, which is SiO _x Negative pole, where 0<x<2.

Preferably, the stirring time in step S2 is 6-8 hours.

Preferably, the conductive agent in step S2 is more than one of Super P, acetylene black, carbon nanotubes or carbon black.

Preferably, the SiO _x in step S2 is 70-80 wt% of the electrode slurry, the conductive agent is 10-20 wt% of the total electrode slurry, and the mixed solution is 5-10 wt% of the electrode slurry.

Preferably, the heating time in step S3 is 120-360 minutes.

A lithium-ion battery silicon-based (SiO _x ) negative electrode is prepared by the method.

Application of the composite binder in lithium ion batteries.

The invention adopts the natural macromolecular protein sericin as the main chain, cross-links with the small molecule citric acid, and obtains the composite binder with a three-dimensional network structure. Under certain temperature conditions, the imino group of sericin will react with the carboxyl group of citric acid to generate a composite binder with a three-dimensional network structure. The sericin in the binder is composed of a large number of amino acids such as serine and aspartic acid with hydrophilic groups in the side chain, which has better dispersibility than the traditional PVDF binder. In addition, the formed three-dimensional network structure is conducive to the transmission of electrons and ions, and also greatly improves the mechanical properties of the binder, so that the electrodes maintain good integrity during cycling. The binder prepared by the method can significantly improve the electrochemical performance of the _SiOx negative electrode of the lithium ion battery, and in addition, the binder has the advantages of simple preparation process, low cost and the like, and can easily meet the requirements of industrialization.

Compared with the prior art, the present invention has the following beneficial effects:

1. The composite binder of the present invention has a three-dimensional network structure. The binder selects the natural polymer protein sericin as the main chain of the binder, and cross-links with small molecule citric acid to precisely control the three-dimensional network structure compound binder. The binder is used in the silicon-based SiO _x electrode, which greatly improves the cycle stability of the SiO _x electrode.

2. The composite binder prepared by the present invention is a water-based binder, which has the advantages of environmental friendliness and low cost. Compared with traditional PVDF, the raw material source is extensive and the price is cheap. Among them, sericin powder is a natural polysaccharide, composed of glycine, serine and other amino acids, rich in carboxyl and amino groups, and has the advantages of low price, good dispersibility and water solubility.

3. The SiO _x of the composite binder of the present invention still maintains good cycle stability under relatively high loads, and has important commercial value.

Description of drawings

FIG. 1 is a graph of the cycle performance of the lithium-ion battery prepared in Application Example 1.

Fig. 2 is a SEM image of the SiO _x electrode after 100 cycles of the lithium-ion battery in Application Example 2.

FIG. 3 is a comparison chart of cycle performance of lithium-ion batteries prepared in Application Example 2 and Comparative Example 1 and Comparative Example 2.

detailed description

The content of the present invention will be further described below in conjunction with specific examples, but it should not be construed as a limitation of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field.

Example 1

A kind of composite binding agent that is used for lithium-ion battery SiO _x negative electrode, described composite binding agent is that sericin powder and citric acid are dispersed in deionized water by mass ratio as 1:1, and obtaining concentration is 20mg/ mL of the mixed solution was in-situ cross-linked at 150°C to obtain a composite binder with a three-dimensional network structure, which was labeled as C-SP-CA.

Example 2

A kind of composite binding agent that is used for lithium-ion battery _SiOx negative electrode, described composite binding agent is that sericin powder and citric acid are dispersed in deionized water by mass ratio as 2:1, and obtaining concentration is 30mg/ mL of the mixed solution was cross-linked in situ at 120°C to obtain a composite binder with a three-dimensional network structure.

Example 3

A kind of composite binding agent that is used for lithium-ion battery _SiOx negative electrode, described composite binding agent is that sericin powder and citric acid are 1.5:1 to be uniformly dispersed in deionized water by mass ratio, obtain concentration and be 25mg/ mL of the mixed solution was in-situ cross-linked at 160°C to obtain a composite binder with a three-dimensional network structure.

Application example 1

1. Evenly disperse sericin powder and citric acid in deionized water at a mass ratio of 1:1 to obtain a mixed solution with a concentration of 20 mg/mL;

2. Add the SiO _x material and the conductive agent Super P into the above mixed solution at a mass ratio of 7:2, and stir for 8-12 hours to obtain a uniform electrode slurry;

3. Coating the electrode slurry on the copper foil, in-situ cross-linking at 150°C to form a composite binder with a three-dimensional network structure, vacuum drying and slicing to prepare SiO _x (0<x<2) negative electrodes electrode sheet.

FIG. 1 is a graph of the cycle performance of the lithium-ion battery prepared in Application Example 1. It can be seen from Figure 1 that the SiO _x (0<x<2) electrode has a discharge capacity of 960mAh g ^-1 after 300 cycles at a current density of 500mAg ^-1 , indicating that the SiO _x anode exhibits excellent cycle stability.

Application example 2

1. Dissolve sericin powder and citric acid particles in deionized water at a mass ratio of 1:1 to obtain a slightly yellowish mixed solution with a concentration of 20 mg/mL;

2. Then add the SiO _x material and the conductive agent Super P into the above mixed solution at a mass ratio of 7:2, and stir for 8-12 hours to obtain a uniform electrode slurry. Wherein, the amount of the mixed solution accounts for 10% of the mass of the electrode;

3. Coat the electrode slurry on the copper foil, heat at 150°C for 120min for in-situ cross-linking to form a composite binder with a three-dimensional network structure, and transfer it to an oven at 80°C to fully dry to obtain SiO _x (0<x< 2) Negative electrode sheet.

4. Transfer the dry negative electrode sheet into a glove box filled with argon, use lithium sheet as the counter electrode, use 1mol/L LiPF ₆ as the solute in the electrolyte, and use EC and DEC with a volume ratio of 1:1 as the solvent, in which 10wt %FEC and 1wt% VC as additives. Use CR2032 button cells for assembly, let the assembled button cells stand for 8 hours, and test the electrochemical performance of the cells in the blue electric test system with a constant current. Due to the cross-linking reaction between sericin (SP) and citric acid (CA), the mechanical strength of the adhesive was strengthened.

Fig. 2 is a SEM image of the SiO _x electrode after 100 cycles of the lithium-ion battery in Application Example 2. It can be seen from Figure 2 that after 100 cycles of the electrode using C-SP-CA binder, the surface of the electrode is smooth without cracks, indicating that the C-SP-CA binder can effectively maintain the integrity of the electrode, thereby improving the electrode’s durability. cycle stability. FIG. 3 is a comparison chart of cycle performance of lithium-ion batteries prepared in Application Example 2 and Comparative Example 1 and Comparative Example 2. It can be seen from Fig. 3 that the SiO _x (0<x<2) electrode prepared with C-SP-CA binder has a discharge capacity of ^1134.4mAh g after 90 cycles at a current density of 200mA g ^-1 or more, while the discharge capacities of only sericin in Comparative Example 1 and carboxymethyl cellulose in Comparative Example 1 were 40.7mAh g ^-1 and 949.4mAh g ^-1 , indicating that the SiO prepared in Application Example 2 The _x electrode has higher specific discharge capacity and better cycle stability.

Comparative example 1

1. Dissolve sericin powder in deionized water to obtain a slightly yellowish mixed solution with a concentration of 20mg/mL;

2. Then add the SiO _x material and the conductive agent into the above mixed solution at a mass ratio of 7:2, and stir for 8-12 hours to obtain a uniform electrode slurry. Wherein, the amount of the mixed solution accounts for 10% of the mass of the electrode.

3. Coat the electrode slurry on the copper foil, and fully dry it in an oven at 80° C. to obtain a negative electrode sheet.

4. Transfer the dry negative electrode sheet into a glove box filled with argon, use lithium sheet as the counter electrode, use 1mol/LLiPF ₆ as the solute in the electrolyte, and use EC and DEC with a volume ratio of 1:1 as the solvent, in which 10wt% FEC and 1 wt% VC were used as additives. Use CR2032 button cells for assembly, and let the assembled button cells stand for 8 hours. The static battery was tested for electrochemical performance by constant current in the blue electric test system.

Comparative example 2

1. Dissolve 20mg of carboxymethylcellulose (CMC) in 1mL of deionized water to obtain a viscous mixed liquid with a concentration of 20mg/mL;

2. Then add the SiO _x material and the conductive agent into the above mixed solution at a mass ratio of 7:2, and stir for 8-12 hours to obtain a uniform electrode slurry. Wherein, the amount of the mixed solution accounts for 10% of the mass of the electrode.

3. Coat the electrode slurry on the copper foil, and fully dry it in an oven at 80° C. to obtain a negative electrode sheet.

4. Transfer the dry negative electrode sheet into a glove box filled with argon, use the lithium sheet as the counter electrode, use 1M LiPF ₆ as the solute in the electrolyte, and use EC and DEC with a volume ratio of 1:1 as the solvent, in which 10wt% FEC and 1wt% VC as an additive. Use the CR2032 button battery for assembly, let the assembled button battery stand for 8 hours, and test the electrochemical performance of the battery in the blue electric test system with a constant current.

It can be shown by the above-mentioned application example 2 and comparative examples 1 and 2 that the C-SP-CA binder of the present invention has good mechanical properties, can ensure the integrity of the electrode in the cycle process, and the prepared SiO _x (0 <x<2) After 90 cycles of the electrode, the discharge capacity can reach more than 1134.4mAh g ^-1 . The prepared SiO _x electrode has a higher discharge specific capacity and better cycle stability. It is bonded with C-SP-CA The _SiOx electrode of the agent exhibits excellent electrochemical performance.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations and modifications made without departing from the spirit and principles of the present invention Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (5)

1. A composite binder for a silicon-based cathode of a lithium ion battery is characterized in that the composite binder is abbreviated as C-SP-CA and is prepared by uniformly dispersing sericin powder in deionized water, adding citric acid to form a mixed solution, and carrying out in-situ crosslinking reaction at 120-160 ℃; the mass ratio of the sericin powder to the citric acid is (1-2) to 1, and the volume ratio of the sericin powder to the deionized water is (20-30) mg to 1mL.

2. The method for preparing the silicon-based negative electrode of the lithium ion battery by using the composite binder as claimed in claim 1, is characterized by comprising the following steps of:

s1, adding sericin powder and citric acid into deionized water, and stirring until the sericin powder and the citric acid are completely dissolved to obtain a mixed solution;

s2, adding an electrode active substance SiO into the mixed solution _x Mixing and stirring the mixture and a conductive agent for 6 to 8 hours to obtain uniformly dispersed electrode slurry; the SiO _x 70-80 wt% of the total mass of the electrode slurry, 10-20 wt% of the total mass of the electrode slurry and 5-10 wt% of the total mass of the electrode slurry;

s3, coating the obtained electrode slurry on a current collector, heating at 120-150 ℃ for 120-360 min, and promoting the sericin powder and citric acid to perform a crosslinking reaction in the heating process to obtain the silicon-based negative electrode of the lithium ion battery, namely the SiO _x Negative electrode of which 0<x<2。

3. The method for preparing the silicon-based negative electrode of the lithium ion battery by using the composite binder according to claim 2, wherein the conductive agent in the step S2 is one or more of Super P, acetylene black, carbon nanotubes or carbon black.

4. A silicon-based negative electrode for a lithium ion battery, wherein the silicon-based negative electrode for the lithium ion battery is prepared by the method of claim 2 or 3.

5. Use of the composite binder of claim 1 in a lithium ion battery.

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